If you've been thinking about making sweatshirts, sweatpants, or any other loungewear, you've probably noticed that there are a LOT of fabrics that seem like they would be great, but they all have different names. So what do those names mean?
This is what people usually think of when they think of sweatshirt fleece. It's a smooth finish on the front, and on the back it's fuzzy and cuddly. In addition to being called Fleece-Backed, it can also be called Sweatshirt Fleece, or sometimes just Fleece.
It's a knit, so the fabric is first knit on a machine, and then to create the soft backing, the back of the fabric is brushed. Using metal wires and combs, the back of the fabric is, essentially, roughed up until it forms a thick, fleecy finish. The finish will vary depending on how much the fabric is brushed; a little brushing leaves a light layer, and a really thorough brushing leaves a thicker, plushier layer. This layer's lofty composition traps air within it, making the fabric very warm and exceptionally soft on the skin.
The downside to all this brushing is that it restricts some of the stretch in the fabric, especially the cross-wise, or horizontal, stretch (the stretch from selvedge-selvedge). This often means that fleece-backed sweatshirt fabric will have a vertical stretch greater than the horizontal, which can affect how the fabric feels on, as well as how it moves.
This is also called loop-backed fleece or looped-back terry fabric. It has the same face, or front-side, as a more traditional sweatshirt fabric. The back side, however, is covered in little loops of thread. These loops can be very small and delicate (this is often called baby terry), or even quite large and shaggy.
These loops help wick away moisture and sweat, which makes french terry a great choice for workout wear. They are also generally quite soft on the skin, and do still help trap warm air (though not to the same degree as a fleece-back fabric). It's a much more breathable sweatshirt option, great for transitional weather or those who get overheated easily.
There is also a heavy knit called a double-faced knit fabric. It's two layers of fabric that have been knit together, so both the face and the reverse side are the smooth finish (like the face on the fleece-backed fabric and the french terry). It's essentially the knit version of a double gauze; two layers that are connected at regular intervals.
This creates a fabric with a little air layer inside, giving it a lot of insulating properties. It's great for those who want an extra-warm fabric, or those whose skin is extremely sensitive to texture.